Most environmental problems exist because adequate measures for preventing them( )taken in the past.

A. are given B. were to be given

C. will be given D. were given

A. when B. than

C. then D. after

A. will greatly increase B. would greatly increase

C. has greatly increased D. would be greatly increased

A. were repaired 　B. will be repaired

C. have been repaired 　D will have been repaired

A. I am to 　　　　　 　　 B. I will

C. I 　　　　　　　　　 D. I am going to

A. will leave B. leaves

C. will have left D. left

A. will leave B. leaves

C. will have left D. left

A. will leave B. leaves

C. will have left D. left

A. It was B. Those are

C. It is D. They have been

A. were being expressed B. are being expressed

C. are expressed D. have been expressed